1. Field of the Invention
The present invention relates to an electric rotating machine, a stator of the electric rotating machine, and an armature winding of the electric rotating machine.
2. Description of the Related Art
A stator of an electric rotating machine is configured as shown in FIG. 25A. FIG. 25A is a sectional view showing a part of the stator of the electric rotating machine wherein a plurality of winding slots 10 are formed in the core 3 of the stator configured with a stacked iron plates and an armature winding 2 is mounted in each winding slot 10. The winding slots 10 are formed in the core 3 in a direction extending along a rotating axis of a rotor (not shown) and a plurality of ventilation ducts (not shown) are provided in a radial direction in the core 3. The armature winding 2 is stored in each winding slot 10.
The armature winding 2 stored in the slot 10 includes a top coil section 2c and a bottom coil section 2d, each of which is composed of a number of stacked strands or element wire conductors 5. Each of the coil sections 2c and 2d is composed of two columns 2c1 and 2c2 each includes a number of stacked conductors 5 as shown in FIG. 25B wherein a part of one coil section 2c is illustrated as an example. The coil sections 2c and 2d are held in the slot 10 by a wedge 3A at the opening part of the slot 10. As shown in FIG. 25B, the conductors 5 in the columns 2c1 and 2c2 are twisted along its lengthwise direction in the slot 10. When the conductors 5 are twisted with a transposing pitch P, the position of the conductor 5 is transposed at 360 degrees, for example, as a typical example between both ends of the slot 10. The other coil section 2d is configured in the similar manner.
Further, the element wire conductors 5 are short-circuited commonly at both side parts of the armature winding 2 to form a half coil having commonly connected end portions configured to protrude to the outside from both side ends of the slot 10 of the core 3, so that the element wire conductors 5 in the half coil are commonly connected in parallel.
In the case where an alternating current flows through multiple element wire conductors 5 in an electric power generator, for example, a leakage magnetic flux F crossing the winding slot 10 in a circumferential direction is generated as shown in FIG. 25A, whereby alternating voltages are induced in the element wire conductors 5. If very large voltages are induced between a pair of element wire conductors in the half coil, for example, a large circulation current, i.e., a current circulating along a closed loop circuit formed by an element wire conductor pair flows, and then, a current loss increases and heat generated inside the element wire conductor pair also increases.
Therefore, in order to substantially equalize the voltages induced in each of the element wire conductor pair so as to prevent the circulation current from flowing, each of the paired element wire conductors is transposed or twisted by such a variety of methods as disclosed in patent documents such as U.S. Pat. No. 1,144,252, 1915 issued to L. Roebel or U.S. Pat. No. 2,821,641, 1958 issued to W. L. Ringland.
Hereinafter, with reference to FIGS. 26 and 27, a description will be given with respect to the transposition method of the element wire conductors that is a conventional technique disclosed in the above patent documents. In transposing the element wire conductors, the element wire conductors are twisted along the longitudinal direction of a winding slot, whereby the positions of the element wire conductors are sequentially changed. In a cross section of the element wire conductors, assuming that a certain element wire conductor pair is rotated around the periphery of the sectional middle of the conductors, a degree of transposition is represented by an angle of the rotation around the longitudinal axis of the conductors. The transposition that a starting position of the element wire conductors at one end in the winding slot comes at a position identical to the starting position at the other end of the winding slot is referred to as a 360-degree transposition (refer to U.S. Pat. No. 1,144,252).
FIG. 26 is a schematic view representing an element wire conductor pair of the 360-degree transposition. One of the element wire conductor pair is shown in FIG. 26 as a conductor which is composed of five conductor sections 5a, 5b, 5c, 5d, 5x and 5y. The conductor sections 5a, 5b, 5c and 5d in the conductor 5 in the stator winding 2 are positioned in the active region or the winding slot 10 formed in the stator core 3 extending along a rotating axis of a rotor (not shown). The conductor in the conductor pair is twisted between the sections 5a and 5b and between the sections 5c and 5d in the winding slot 10 by 180 degrees, respectively, so that the conductor is transposed at 360 degrees in the winding slot 10. Both ends of the element wire conductor 5 shown as the sections 5x and 5y are extended outside the slot 10. Though not shown in the figure, the sections 5x and 5y are connected with corresponding end sections of another element wire conductor (not shown) in the conductor pair so that the conductor pair including the conductor 5 is connected in parallel with each other at both ends of a half coil of the armature winding 2 protruding to the outside from both sides of the slot 10 to form a closed circuit loop as a strand pair.
In the configuration shown FIG. 26 it is assumed that magnetic fluxes 16a to 16d interlink with the sections 5a to 5d of the conductor 5 in the slot 10. In the figure, the magnetic flux 16a interlinks the section 5a, the fluxes 16b and 16c interlink the section 5b and 5c, and the flux 16d interlinks the section 5d. Fluxes 16x and 16y also interlink the outside sections 5x and 5y of the conductor 5, respectively. At an instant period of time, the fluxes in the figure interlink in the normal direction to the drawing paper in one direction. When the conductor 5 is twisted by 180 degrees, the symbol “x” in the circle shown in the figure denotes the orientation of the fluxes passing from the top to back surface of the drawing paper and the symbol “.” in the circle denotes the orientation from back to top surface of the drawing paper. The magnetic fluxes 16a to 16d and 16x and 16y are generated at a moment at which a given current has flowed through the twisted element wire conductor 5 so as to denote directions of the induced voltages caused by the current flowing through the sections 5x to 5y of the conductor 5. For example, in FIG. 26, a configuration is given such that an absolute value of the sum of fluxes 16a and 16d is equal to that of the fluxes 16b and 16c, so that the induced voltages in the sections 5a and 5d are canceled by the induced voltages in the section 5b and 5c in the winding slot 10.
However, although a 360-degree transposition is applied in the conductor positioned in the winding slot 10 as disclosed above, no transposition is performed outside of the winding slot 10 with respect to the sections 5x and 5y in the conductor 5. Therefore, unbalanced voltages will be generated by means of leakage magnetic fluxes 16x and 16y at the both end parts outside the stator core 3, and a circulation current will be generated in the closed circuit formed by the element wire conductor 5 and another conductor (not shown) connected in parallel with the conductor 5 at both ends thereof forming a conductor pair.
As has been described above, the leakage magnetic fluxes 16x and 16y exist at the external of the stator core 3, whereby unbalanced voltages are induced to the end parts of the winding conductor 5 as well as the end parts of the conductor connected in parallel to the conductor 5, a circulation current flows in the closed circuit formed by the element wire conductor pair, and then, a current loss occurs. In order to reduce this loss, the positions of the element wire conductor 5 at both ends thereof should be transposed by 180 degrees, so that the directions of voltages induced at both end sections 5x and 5y of the same element wire conductor 5 are opposed, whereby they may be canceled or offset. This can be achieved by making the element wire conductor pair a 540-degree transposition in the winding slot 10, i.e., making the element wire conductor pair 5 a transposition of one rotation and a half, namely a 540-degree transposition (refer to U.S. Pat. No. 2,821,641), provided that the leakage flux 16x is equal to the flux 16y. Now, the 540-degree transposition will be described by referring to FIG. 27.
FIG. 27 is a schematic view representing an element wire conductor pair of a 540-degree transposition. Like constituent elements of FIG. 26 are designated by like reference numerals, and a duplicate description is omitted here in FIG. 27.
In FIG. 27, transposing pitches in two ranges of ¼Ls of the core length Ls on both side regions of the stator core 3 (left side core border zone and right side core border zone) are the half of the range of ½Ls of a core length Ls of the winding slot 10 in the core 3. Namely, the transposing pitch of the middle zone is 1, whereas the transposing pitches in the core border zones are ½, and a 180-degree transposition is made at each one of both border zones 4A, 4B and the middle zone 4C of the core 3. A sum of the interlinking magnetic fluxes 16a and 16e in the element wire conductor sections 5a and 5e included in the border zones 4A, 4B is equal to the flux 16c in the section 5c included in the middle zone 4C, and a sum of fluxes 16b and 16f in the sections 5b and 5f in the border zones 4A, 4B is equal to the flux 16d in the section 5d in the middle zone 4C, and thus, the inductive voltages induced in the conductor sections 5a to 5f positioned in the winding slot 10 are offset. In addition, in the outside of the winding slot 10, the voltages induced by the magnetic fluxes 16x and 16y interlinking with the outside sections 5x and 5y also offset, respectively, so that the circulation current exerted by the leakage magnetic fluxes at the end parts of the conductor 5 can also be reduced or minimized in the closed circuit formed by a conductor pair including the conductor 5.
With respect to the armature winding and a field winding of an electric rotating machine, since each conductor 5 forming the armature coil 3 is coated with an insulation material, an upper limit of a temperature is strictly limited by the heat resistance performance of the insulation material used for configuring these winding conductors. In designing the electric rotating machine, it is necessary to make a design so that these temperatures are maintained at or below the rated value.
In the conventional technique described above, when the transposing angle of the element wire conductors shown in FIG. 27 is set at 540 degrees, in the case where the leakage magnetic fluxes at both end sections 5x and 5y are equal to each other, the induced voltages generated at both ends of the element wire conductor pair are offset ideally. However, in the case where the amount of the magnetic fluxes interlinking the element wire conductor pair at both end sections 5x and 5y are different from each other, the inductive voltages induced at the end sections external to the core 3 cannot be completely offset. Examples of the cases are shown below.
For example, as shown in FIG. 28, lengths Xc and Xt of coil end parts extending in an axial direction from side ends of the stator core 3 are different from each other. Further, as shown in FIG. 29, a half coil 2c of the armature winding 2 protruding from a left end of a first slot of the stator core 3 is connected with another half coil 2d which is held in a second slot of the stator core 3 and, the other end of the half coil 2d protruding from the other end of the core 3 is connected to further half coil 2e which is held in a third slot which is different from the first slot in which the half coil 2c is held. Thus, a distance βc between the second and third slots in the right side of the half coils 2d and 2e is shorter than the distance βt between the first and second slots in the left side of the core 3.
In the case of FIG. 29, the third slot in which the half coil 2e enters may be a near slot close from the first slot in which the half coil 2c is held in the right side and the distance between the slots may be separated by two or more slots. The distance between the slots may be determined depending on connection of the coils of the armature winding, and the lengths of the end part of the coils outside the slot of the core 3 are different from each other. This fact causes the quantities of magnetic fluxes incident to the end part of the coils protruding outside the core 3 to be different between the one connection side and the other connection side of the armature winding 2.
In addition, as schematically shown in FIG. 30, at a connection part outside the slot 10 of the core 3, because of a connection from a load terminal of the electric rotating machine to a connection terminal of the armature winding or a connection terminal with an external parallel circuit, the element wiring conductors 5 of the armature winding 2 are connected to a connection copper band 12. A current flows also in this connection copper band 12, and thus, a magnetic flux is generated. If this externally generated magnetic flux is incident to the end part sections of the conductors 5, an interlinking magnetic flux 16x at the left side and an interlinking magnetic flux 16y at the right side cannot be offset completely.
FIG. 31 shows an example of a distribution of a loss that occurs in the twisted element wire conductors of a turbine power generator, the loss being obtained by means of numeric analysis. The figure shows examples of loss distributions in a case in which the interlinking magnetic flux quantities at both ends of the conductors are equal to each other (shown by a dashed line) and in a case in which the interlinking magnetic flux quantities at both ends are different from each other (shown by a solid line). It is found that, in the case where the flux quantities are different at both ends, a maximum value of an element wire loss increases as shown by the solid line because an unbalanced voltage is generated between element wire conductors and a circulation current flows. How much the maximum value of the element wire conductor loss increases depends on a design such as a structure of an electric rotating machine or a level of a current flowing in the winding of the electric rotating machine. In addition, the magnetic flux levels incident to the end part sections of the conductors are different from each other even between top and bottom coils as shown in FIG. 25, and thus, losses are different from each other. Further, the difference may occur also depending on the peripheral position of an armature-winding bar.
If the quantities of the interlinking magnetic fluxes incident to the element wire conductors at both end parts of the element wiring conductors are thus different from each other, the inductive voltages induced in the element wire conductors are not completely offset, a circulation current flows in the element wire conductor pair, and a loss occurs, thereby causing local overheat or lowered efficiency in the electric rotating machine.